Injections often require that the fluid of interest be drawn from a vial containing the fluid into a syringe prior to delivery via a needle. Drawing the fluid from the vial can be done using an empty syringe or a syringe filled with a volume of air equal to the desired volume of fluid to be withdrawn. In the latter instance, removal of fluid using an empty syringe is difficult because of the increased pressure within the vial and often results in the withdrawal of air into the syringe and loss of fluid when the needle is withdrawn from the vial. In the former, a small amount of air is drawn into the syringe due to the dead space within the needle itself. In the context of injections for medicinal use, injection of air can be both painful and dangerous to a patient, and current practice involves removal of the bubbles prior to injection. Elimination can be accomplished by flicking the syringe to get the bubbles to pool at the top of the barrel followed by depression of the plunger to expel the air.
Since there is usually no definitive means to determine the exact point at which all air has been evacuated, there is unnecessary loss of fluid as the user must overcompensate in depressing the plunger until a small amount of fluid is expelled from the chamber. Besides the cost of the wasted drug, this process has a few other problems as well. The excess fluid could prove to be harmful if it is absorbed as a result of contact with the skin or mucous membranes. Due to these concerns, the bubble-removal process can be both time consuming and stressful: a user must continuously check the syringe barrel to ensure no air is in the chamber, while moving the plunger slowly enough to ensure minimal fluid loss. Additionally, this process can be time-consuming as the user must check the barrel continuously to determine that no air remains in the barrel.